Audio compressor for scanner

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w2aew

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A friend asked me recently if I could come up with a circuit that he could use with his scanner to equalize the volume of the various stations he receives on his scanner. He was frustrated by the fact that if he turned up the volume to hear the "quiet" signals (narrow modulation, etc.), that he would then get blasted by the loud signals.

I came up with a fairly simple circuit. The input comes from the speaker-out of the scanner. The output of the circuit is a low-level, high-impedance output, designed to be put into an audio amplifier (since his plan was to use an audio distribution amplifier anyway).

I have two videos that describe the circuit. The first is on the bench, describing the schematic and demonstrating its operation using a signal generator. The second video shows the circuit in use with a scanner.

Here are the video links:

Circuit fun: Automatic audio leveling circuit | audio compressor | for scanning receiver - YouTube

Automatic Volume Level Control circuit demonstration | scanner - YouTube

I hope you find this useful.
 

K9DAK

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Brilliant! I'll be building two of these, one for each side of my stereo feed.

I could see making a PCB with two of these on it, putting it in an enclosure with appropriate input and output jacks, and powering it with a 9-12V wall wart.

It could serve two functions at once for a feed . . . volume leveling and external speaker level to line level conversion. Nice!

Any chance of posting a pdf of the schematic?
 
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w2aew

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Brilliant! I'll be building two of these, one for each side of my stereo feed.

I could see making a PCB with two of these on it, putting it in an enclosure with appropriate input and output jacks, and powering it with a 9-12V wall wart.

It could serve two functions at once for a feed . . . volume leveling and external speaker level to line level conversion. Nice!

Any chance of posting a pdf of the schematic?
Another fellow ham, SM6XUN already created a PCB and has shared it on OSH Park. See his posting in the eham thread here:
Automatic audio leveling circuit

Here's the direct link to the PCB:
https://oshpark.com/shared_projects/gIatmFI5
 

radioman2001

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Very nice, what components would I have to change to make this work in a real radio. I have a few analog and digital Astro Spectra radios, and this is a real problem when switching from ham and weather channels which are wide 5kc audio and Fire which are 2.5kc audio. I plan on breaking connection inside the radio and put it in series just before the audio amp.

What was the price for the circuit boards, I know shipping is the US is free.
 

w2aew

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Very nice, what components would I have to change to make this work in a real radio. I have a few analog and digital Astro Spectra radios, and this is a real problem when switching from ham and weather channels which are wide 5kc audio and Fire which are 2.5kc audio. I plan on breaking connection inside the radio and put it in series just before the audio amp.

What was the price for the circuit boards, I know shipping is the US is free.
It's difficult to say without knowing the signal level at the point where you want to insert this circuit. The circuit starts the compression action when the peak-peak input level is a few hundred mVpp or more. If the level at the point where you want to put this circuit in-line isn't this large, then you'll have to amplify it. Also, you have to consider what signal level is needed to drive your audio amplifier. If the output of this circuit is too low, you may need to add a preamp before going into the audio amp.
 

oilmillcharlie

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I would love to buy one since I am not very good at circuit board assembly. If anyone is building one for sale or otherwise I would like to get one assembled.
 

K9DAK

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Charlie . . . I'll build one for ya.

I ordered three boards (the minimum order) but I only need two, for a stereo feed. I'd be happy to build up my third one for you. I was wondering what I was going to do with the extra one anyway! :)

Can't tell ya when exactly I might build them as I have a lot of other things going on yet this summer, but I'll bet I could knock one out during a Bears game after Labor Day.
 

oilmillcharlie

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Charlie . . . I'll build one for ya.

I ordered three boards (the minimum order) but I only need two, for a stereo feed. I'd be happy to build up my third one for you. I was wondering what I was going to do with the extra one anyway! :)

Can't tell ya when exactly I might build them as I have a lot of other things going on yet this summer, but I'll bet I could knock one out during a Bears game after Labor Day.

Sounds good keep me posted. Thanx
 
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